Methods of providing article with corrosion resistant coating and coated article

Abstract

According to the invention, an article that is exposed to high temperature e.g., over 1000° C. during operation is disclosed. In one embodiment, a method for a gas turbine engine includes a directionally solidifed metallic substrate, e.g., a superalloy, which defines an airfoil, a root and a platform located between the blade and root. The platform has an underside adjacent the root, and a corrosion resistant overlay coating such as an MCrAlY or a noble metal containing aluminide or corrosion inhibiting ceramic is located on portions or the blade not previously covered with such coatings, e.g., the underside of the platform and the neck. The applied coating prevents corrosion and stress corrosion cracking of blade in these regions. Where the airfoil is also created, the airfoil coating may have a composition different from that of the coating on the underplatform surfaces.

What is claimed is:  
     
         1 . A method of improving the durability of a turbine blade composed of a superalloy material and defining an airfoil, a root, a neck, and a platform located between the airfoil and root, the platform has an underside adjacent the neck, comprising the steps of: 
 providing a superalloy substrate; and    applying a corrosion resistant overlay coating to the underside of the platform and blade neck.    
     
     
         2 . The method of  claim 1 , wherein the coating applied is an MCrAlY overlay coating (M representing combinations of Ni, Co and/or Fe).  
     
     
         3 . The method of  claim 1 , wherein the coating contains 10-40%, Cr, 5-35% Al, 0-2% Y, 0-7%, Si, 0-2% Hf, balance primarily Ni and/or Co with all other elemental additions comprising <20% of the total.  
     
     
         4 . The method of  claim 1 , wherein the coating contains 20-40% Cr, 5-20% Al, 0-1% Y, 0-2% Si, 0-1% Hf, balance primarily Ni and/or Co with all other elemental additions comprising <20% of the total.  
     
     
         5 . The method of  claim 1 , wherein the coating contains 25-40% Cr, 5-15% Al, 0-0.8% Y, 0-0.5% Si, 0-0.4% Hf, balance primarily Ni and/or Co with all other elemental additions comprising <20% of the total.  
     
     
         6 . The method of  claim 1 , wherein the coating is applied to a nominal thickness of less than about 0.005″.  
     
     
         7 . The method of  claim 1 , wherein the coating is applied to a thickness between about 0.005-0.003″.  
     
     
         8 . The method of  claim 1 , further comprising the step of applying another coating on the airfoil surface.  
     
     
         9 . The method of  claim 8 , wherein the composition of the another coating being different than the corrosion resistant overlay coating.  
     
     
         10 . The method of  claim 1 , further comprising: an aluminide layer on the substrate surface, the overlay coating on the aluminide layer.  
     
     
         11 . The method of  claim 1 , further comprising an aluminide layer located on the overlay coating.  
     
     
         12 . The method of  claim 1 , wherein the step of providing a substrate includes providing a substrate comprised of an equiaxed nickel-based alloy, a directionally solidified nickel-based alloy, a single crystal nickel-based alloy or a columnar grain nickel-based alloy.  
     
     
         13 . The method of  claim 1 , wherein the step of applying the coating is performed by cathodic arc, thermal spray, vapor deposition or sputtering.  
     
     
         14 . A method of improving the durability of a superalloy gas turbine component which operates in an environment with primary gas path temperatures in excess of 1000° C. The method having a first, exposed portion which is directly exposed to hot gas path, a second, shielded section which is shielded from direct exposure to the hot gas path, and a third section between the exposed and shielded portions, the improvement which comprises applying a corrosion resistant overlay coating applied to the third section.  
     
     
         15 . The method of  claim 14  wherein the component comprises a turbine blade, the first portion forming an airfoil, the airfoil covered by a first coating, the second portion forming a root, and the third section forming a platform and neck, the improvement comprising a corrosion resistant coating applied to the underside of the platform and neck.  
     
     
         16 . The method of  claim 14 , further comprising the step of applying another coating on the airfoil surface.  
     
     
         17 . The method of  claim 18 , the composition of the another coating being different than the corrosion resistant overlay coating.  
     
     
         18 . The method of  claim 14 , wherein the step of applying includes applying an MCrAlY coating (M representing combinations of Ni, Co and/or Fe).  
     
     
         19 . The method of  claim 14 , wherein the coating in weight percent contains 10-40% Cr, 5-35%, Al, 0-2% Y, 0-7% Si, 0-2% Hf, balance primarily Ni and/or Co with all other elemental additions comprising about <20% of the total.  
     
     
         20 . The method of  claim 14 , wherein the coating contains 25-40 %, Cr, 5-15% Al, 0-0.8% Y, 0-0.5% Si, 0-0.4% Hf, balance primarily Ni and/or Co with all other elemental additions comprising about <20% of the total.  
     
     
         21 . The method of  claim 14 , wherein the coating has a nominal thickness of less than about 0.005″.  
     
     
         22 . The method of  claim 14 , wherein the step of applying the coating is performed by cathodic arc, thermal spray, vapor deposition or sputtering.  
     
     
         23 . A method of improving the durability of a turbine blade composed of a superalloy material and defining an airfoil, a root, a neck, and a platform located between the airfoil and root, the platform has an underside adjacent the neck, comprising the steps of: 
 providing a superalloy substrate; and    applying a corrosion resistant noble metal-containing aluminide coating on the underside of the platform and blade neck.    
     
     
         24 . The method of  claim 23 , wherein the step of applying an aluminide coating includes applying a platinum aluminide coating.  
     
     
         25 . The method of  claim 23 , wherein the coating contains about 11-60 wt. % platinum, balance aluminum.  
     
     
         26 . The method of  claim 23 , wherein the coating contains about 25-55 wt. % platinum, balance aluminum.  
     
     
         27 . The method of  claim 23 , wherein the coating contains about 30-45 wt. % platinum, balance aluminum.  
     
     
         28 . The method of  claim 23 , wherein the coating has a nominal thickness of less than about 0.005″.  
     
     
         29 . The method of  claim 23 , further comprising the step of applying another coating on the airfoil surface.  
     
     
         30 . The method of  claim 29 , the composition of the another coating being different than the corrosion resistant noble metal containing aluminide coating.  
     
     
         31 . The method of  claim 23 , wherein the step of applying the coating is performed by electroplating the noble metal onto the substrate; and 
 aluminizing the substrate.    
     
     
         32 . A method of improving the durability of a superalloy gas turbine component which operates in an environment with primary gas path temperatures in excess of 1000° C., the component having a first, exposed portion which is directly exposed to hot gas path, a second, shielded section which is shielded from direct exposure to the hot gas path, and a third section between the exposed and shielded portions, the improvement which comprises applying a corrosion resistant aluminide coating applied to the third section.  
     
     
         33 . The component of  claim 32  comprising a turbine blade, the first portion forming an airfoil, the section portion forming a root, and the third section forming a platform, the improvement comprising a corrosion resistant coating applied to the underside of the platform.  
     
     
         34 . The method of  claim 32 , further comprising the step of applying another coating on the airfoil surface.  
     
     
         35 . The method of  claim 32 , wherein the step of applying another coating includes applying another coating having a composition different than the noble metal containing aluminide coating.  
     
     
         36 . The method of  claim 32 , wherein the coating further comprises yttrium, hafnium and/or silicon.  
     
     
         37 . A method of improving the durability of a turbine blade composed of a superalloy material and defining an airfoil, a root, a neck, and a platform located between the airfoil and root, the platform has an underside adjacent the neck, comprising the steps of: 
 providing a superalloy substrate; and    applying a corrosion inhibiting, ceramic overlay coating on the underside of the platform.    
     
     
         38 . The method of  claim 37 , wherein the ceramic coating is composed of stabilized zirconia.  
     
     
         39 . The method of  claim 37 , wherein the ceramic is applied by vapor deposition, thermal spray, or sputtering.  
     
     
         40 . The method of  claim 37 , wherein the ceramic coating is applied to a nominal thickness of less than about 5 mils.  
     
     
         41 . The method of  claim 37 , wherein the step of applying includes forming an alumina layer on the substrate surface, the ceramic coating on the alumina layer.  
     
     
         42 . The method of  claim 37 , wherein the alumina layer is formed from an aluminide or overlay bond coat applied to the substrate.  
     
     
         43 . The method of  claim 37 , further comprising the step of applying another coating on the airfoil surface.  
     
     
         44 . The method of  claim 43 , wherein the step of applying another coating includes applying another coating having a composition different than the ceramic coating.  
     
     
         45 . A method of improving the durability of a superalloy gas turbine component which operates in an environment with primary gas path temperatures in excess of 1000° C., the component having a first, exposed portion which is directly exposed to hot gas path, a second, shielded section which is shielded from direct exposure to the hot gas path, and a third section between the exposed and shielded portions, the improvement which comprises applying a corrosion resistant corrosion inhibiting ceramic coating applied to the third section.  
     
     
         46 . The method of  claim 45  comprising a turbine blade, the first portion forming an airfoil, the second portion forming a root, and the third section forming a platform, the improvement comprising a corrosion resistant coating applied to the underside of the platform.  
     
     
         47 . The method of  claim 45 , wherein the ceramic coating is composed of stabilized zirconia.  
     
     
         48 . The method of  claim 45 , wherein the ceramic is applied by vapor deposition, thermal spray, or sputtering.  
     
     
         49 . The method of  claim 45 , wherein the ceramic coating is applied to a nominal thickness of less than about 5 mils.  
     
     
         50 . The method of  claim 45 , wherein the step of applying includes forming an alumina layer on the substrate surface, the ceramic coating on the alumina layer.  
     
     
         51 . The method of  claim 45 , wherein the alumina layer is formed from an aluminide or overlay bond coat applied to the substrate.  
     
     
         52 . The method of  claim 45 , further comprising the step of applying another coating on the airfoil surface.  
     
     
         53 . The method of claim  52 , wherein the step of applying another coating includes applying another coating having a composition different than the ceramic coating.